This invention relates to a variable displacement pump which is applied, for example, to a hydraulic pressure source for supplying hydraulic oil to various sliding sections and the like of an automotive internal combustion engine, and more particularly to the variable displacement pump whose discharge amount (discharge pressure) is variable in accordance with engine operating conditions.
As a conventional variable displacement pump to be used for an oil pump of an automotive vehicle, there is proposed one disclosed in International Application Publication (Tokuhyou) No. 2008-524500. In summary, this variable displacement pump is of a so-called vane type and arranged such that a discharge pressure is selectively supplied to two pressure chambers defined between a housing and a cam ring so as to control the eccentricity amount of the cam ring which is always biased in a direction to be eccentric relative to the center axis of a rotor, thereby rendering the discharge amount (discharge pressure) variable.